This first cycle Ring-billed Gull Larus
delawarensis was photographed in December and
is, in my experience, towards the extreme in terms of the extent
of brown on the body and underwing - but its most interesting
feature is the wing coverts; every one is solidly-centered, with
a fringe that is matched by some Mew Gulls and many nominate
Common Gulls. I feel that the much-vaunted difference in covert
pattern can be misleading, as a few RBGUs can have a pattern
very similar to most MEGU/COGU, while a few MEGUs and even more
COGUs can have a pattern similar to some (poorly-marked) RBGUs: